1. Field of the Invention
This invention relates to a diagnostic agent for osteoporosis which comprises a mammalian bone sialoprotein and a method for diagnosis of osteoporosis using the same. More particularly, this invention is concerned with a new immunochemical diagnostic agent and a new method for diagnosis, which can make pathogenetic classification of osteoporosis feasibility. Moreover, there may be suggested a different therapy from the prior ones, e.g., utilization of an immunosuppressing agent, to osteoporotic patients classified according to the present method.
2. Description of the Prior Art
Degenerative osteoporosis is a syndrome showing a reduced amount of bone owing to unknown causes with aging after growth period and subsequent clinical pictures such as easy fractures of bones, lumbago and dorsalgia and the like. As the diagnostic methods for osteoporosis presently applied, there may be mentioned X-ray photographing of bones (MD method), DPA (Dual Photon Absorptiometry), DEXA (Dual Energy X-ray Absorptiometry), CXD (Computed X-ray Densitometry) and determination of a bone mineral amount, a bone density and the like by means of a physical apparatus for determining a bone amount using a low-frequency ultrasonic wave and the like. To determine a bone amount of an individual at a certain age according to such diagnostic methods makes it feasible to judge a person of his or her any future possibility of fractures. More specifically, a remarkable reduction in bone density could suggest a high risk of fractures in the future.
It has been considered, however, that a reduced bone density is only one of dangerous factors for possible fractures and a fracture risk would be also increased owing to phenomena with aging such as a lowered elasticity of collagen fibers, qualitative deterioration of the bone structure, lowered muscular power and so on. These dangerous factors other than lowered muscular power could not presently be determined noninvasively, which remains as an important problem to be solved in the future.
On the other hand, a noninvasive method for determining a bone density, which is a main diagnostic method for osteoporosis, and an invasive method for determining a bone form by biopsy have recently been developed remarkably. However, each of these methods alone may not satisfy all the clinical requirements, so that the most preferred determination method may be selected in compliance with the purpose and any optional combination therewith may be attempted under the present conditions.
The maximum bone density for an individual is attained at ages of 30-40, which is referred to as the peak bone mass. A risk for fractures should be evaluated upon the duration and the rate wherein the peak bone mass could be reduced, but it is impossible to determine bone density retroactively and one should evaluate upon an absolute value when determined. Accordingly, any qualitative changes in bone when a bone density is to be determined or in the very near past could not be determined by the prior non-invasive determination method.
In order to supplement such drawbacks in the current bone density determination methods, attempts have been made to understand pathosis by determining a blood concentration or a urinary excretion level of a bone metabolism controlling factor (parathyroid hormone; PTH), an activated vitamin (1, 25(OH).sub.2 D.sub.3), calcitonin and the like), or various factors liberated from bone tissues with bone metabolic remodeling (alkaline phosphatase, acid phosphatase, pyridinoline, deoxypyridinoline, type-1 procollagen peptide, osteocalcin and the like), but there remain many points unsatisfied.
As regressive osteoporosis is a syndrome which is defined to be a reduced bone amount due to unknown causes, a pathogenetic diagnosis has not been attempted. In other words, the secondary osteoporosis with identified pathogenesis has hitherto been excluded from regressive osteoporosis. This invention is directed to an epoch-making diagnostic method which can classify a part of osteoporosis due to unknown causes as one of autoimmune diseases.